A corpora



Eatcnted Apr. 5, 1927.

SAMUEL E. SHEPPARD AND REUBEN F.

1 tenses PATENT @ltFll CE.

PUNNETT, OE ROCHESTER, NEW YORK, AS-

SIGNORS TO EASTMAN KODAK CQMPANY, OF ROCHESTER, NEW YORK, A CORPORA- TION OF NEW YORK.

PHOTOGRAPHIG EMULSlON AND IVIA'IERIAL AND PRQCESS USED IN THE PREPARA- TIQN THEREOF.

No Drawing.

This invention relates to photographic emulsions, and to materials and processes used in preparing the same.

One object of the invention is to provide. photographic emulsions, especially developing-out ones, having new orimproved properties because of the use or presence therein of materials, the sensitizing properties of which we have discovered. Still another object of our invention is to provide processes in which such materials are used to improve photographic emulsions, especially developing-out ones, as regards light-sensitiveness, by which term we include their ability to give the earliest visible impression or image with the minimum exposureor their ability to give density after a given exposure or both, the usual photographic fluid treatments being used in preparing such impression or image or density.

A further object of the invention is to provide colloid products, such for instance, as gelatins, the usefulness of which for forming light sensitive photographic emulsions, especially developing-out emulsions, is greatly increased and controlled by our said sensitizing materials incorporated therewith. Another object of the invention is to provide processes for preparing said colloid products or intermediates.

Other objects are,-to increase the sensitiveness of photographic emulsions, especially developing-out emulsions, while wholly or partially dispensing with expensive or long and uncertain so-oalled ripening methods; to enable the use of a type of gelatin having desirable physical qualities in making such a photographic emulsion of greater light-sensitiveness than that normally obtainable with said gelatin; to obtain more stable emulsions through the purity of the ingredients; to increase the light-sensitiveness of photographic emulsions, particularly developing-out ones, the grain characteristics of which have already been determined; to increase the general light-sensitiveness of such photographic emulsions throughout the spectral ranges to which they are normally sensitive; to make such photographic emulsions of standard light-sensitive characteristics with gslatins Serial No. 37,522.

which normally do not produce emulsions having such characte-istics; to make, as intermediates in the manufacture of photographic omulsions, gelatins of standard light-sensitiveness giving power out of gelatins which do not normally have the power of giving such standard sensitiveness to emulsions, such as developing-out ones, made from them. Further objects will hereinafter appear.

In United States Patent No. 1,574,944, hilarch 2nd, 1926. S. E. Sheppard photographic light-sensitive material and process of making the same, there is disclosed the remarkable sensitizing properties of certain compounds, when employed in the proper proportions in photographic emulsions, especially developing-out ones, and when employed in gelatin or other colloids for use in making such emulsions. Each member of these series of compounds contains a divalent atom of the sulfur group (a sulfur atom, or a selenium atom, or a tellurium atom), which is joined by a double bond to a single metalloid atom (not one bond to one atom and the other bond to a different atom) to which at least another group of atoms is attached. The metalloid atom to which the atom of sulfur, selenium, or tellurium is joined by a double bond is in many instances a carbon atom. These substances include thiocarbamids, selenocarbamids and tellurocarbamids. The corresponding carbimids are also usable. Various organic groups can be substituted in such carbamids and carbimids.

Examples of such substances are; thio-sinamine (allyl thiourea), allyl isothiocyanate, phenyl isothiocyanate, phenyl thiourea, thiocarbanilide, thiourea, thiosemicarbazide, sodium thiosulfate, (but not sulfate or sulfite) di-otolyl thiourea, seleno-musta-rd-oil (allyl isoseleuocyanate), potassium selenocyanide, allyl selenourea, thioaoetamid, thioformamid, thiobarbituric acid, telluro-mustard-oil (allyl isotellurocyanate) potassium tellurocyanide, allyl tellurourea. It is preferable to use these compounds insubstantially pure or GP. form; but impurities, which are harmless to tl emulsion and are not bulky can be tolerated The selenocyanide ans.

tellurocyanide are used in higher proportions thanthe other listed compounds.

\Vehare found that these substances may be usefully supplemented by reducing agents. These reducing agents are of such anature, and are used in such proportions,

*th at ifthey were present alone in a developing-out emulsion, they would produce a slight fogging action and would not usefiilly increase the sensitivity. lVhen, however, these reducing agents are incorporated with the sensitizing materialsancntioned.

above, they assist the latter in creating or increasing thesensitivity bl the emulsion. When incorporated with-the sensitizing substances in :gel-atin,-tl1ey usefully assist in reinforcing or increasing the powerof the --gel atin to ve sensitive emulsions.

' There-are numerous kinds of reducers which-may be used auxiluiriesto the sensitizers, which :latter arenot reducers otthe silver salts inithe emulsion inthe ordinary sense. Typical reducer-stare the-alkaline salts "of arsenious 'ZlClCl, alkalme hyposulfites,

alkalineh-ypophosphites hydroxylami-ne and tizi ng agent varies-when used alone. But

inigeneralithe quantities ot-reducer which arepermissible-in conjunction with thesen-. -s1tiz1ng substance are o't the same order of magnitude as the latter. Preferably we use equimolecularsparts of-sensitizer and reducer. In any event the amount of reducer is such that the tog in the final emulsion: is belowthe manufacturing tolerance. -In gelatino-silver halid developing out emulsions, 'we employ approximately '10 igrainsor lessof active sensitizing C(Hnj'JOlllltl, such as tlllOSlllflITlllleJITOI" example, in 130 poundsmf emulsion v(the latterlieing computed as the weightof its nc -aqueous ingredients in the dry state). .This amounts .am'ount ot' reducer is,- therefore, generally -lessthan 10 grains in+130 pounds of emulsion or less than lO rrains in 1:00 pounds of gelatin. We have foundil to 3. grains of "sensitizing compound, such as throsmanune,

for instance, and. 2 to 3: grains of a reducer, 1 su'chas sodium 'hyposullite for instance, to

JOOpounds-otgelatin (computed as dry) or i 130 poundsof emulsion (computed asdry) --is Within themseful ilimits andugenerallyex- 'cellent sfor example, with. alkaline develo i ing-out gelatinosilver-halicl emulsions.

course, smaller amounts of sensitizer and reducer are employed when less sensitizing effects are desired; but it is important not to exceed the upper or fogging limits, as indicated above. It is to be noted that we use the term hyposultite in its correct scientific senseaud not as misapplied to sodium *thiosulfate, -as-is sometimes done in the photographic literature.

The amounts of the sensitizer and reducer which are used together in 'theelnulsi'on' are so small that the addition of them does not appreciably dilute the emulsion or the emul- SlOIl-TOllTliIlQ' colloid; nor does it ailccttheir physical (properties. This enables us to se- -lect .gela'tins, for instance, because of their physical properties like setting ability. meltii'igapoints and .viscosity, without regard I to whet-her they ea 11 be made into suiliciently light-sensitive emulsions, and any deficiency in sensitizing power can be made up by incorporating a proper, but wery small quantity," ot' the *sensitizer with the reducer. Such additions do .not effect thegrain size characteristics, which are thus susceptible of independent control.

The effect of using these sensitizers in conjunction with reducers of the typeindicated above, is to produce chemical sensitization, insteadof an optical one. In -other words the etiectvis unlike that of senksitizing dyes, the sensitiv'eness being. increased throughout the normal spectral range of the emulsion instead of at only those"spectralhpoints corresponding to the spectral absorption'of the sensitizing compound and reducer. But,of course, we can =use thesensitizersin conjunction with our reducers in increasing the general light-sen- U sitive-ness ot orthochromatic, panchromatic, iX -r ay and special-emulsions,-as well as the ordinary ones.

We may .usethesensitizers in conjunction with our -reducers in many ways, the uses of this combination being similar to those enumerated for the sensitizers alone in the "above cited application. Broadly they may be incorporated in; emulsions or iu colloids for emulsions or in both. They maybe added .atdiflerent stages of emulsion manufacture, even when the latter is otherwise ready for coating.

The following.example illustrates how light-sensitive photographic emulsions oi the developing-out type may be prepared and improved by the aid of our combination of sensitizeiiand inducer. Otcourso, our invention is not restricted to this illustration except as indicated inthe claims. The emulsion forming operations hereinafter described are along the lines of known p actice, as described in .the-iliterat-in'e ofthe art.

The two following solutions are made up, .the parts being by weight:

v i A. QOOparts of silver nitrate in 9,200parts of water.

B. 690 parts of potassium bromide and 50 parts of potassium iodide in 6,100 parts of water along with 300 parts of gelatin.

emulsion jelly.

In mixing B, the halid salts are first dissolved, the water and the gelatin then added to thesalt solution. Solution B is then warmed, say to 140 F. or 150 F. for example; and the silver nitrate solution A is gradually added to it with constant stirring. It is preferable to warm solution A before adding it to B, say to 150 F. or 160 F. for instance. When solution A has been thoroughly incorporated in solution B, there are then added 43 parts of strong ammonia previously dissolved in 900 parts of water. The emulsion formed by these operations is allowed to stand for a short time, say 15 minutes to a half hour for example. Then 1050 parts of gelatin are dissolved in it with thorough mixing. The emulsion is next cooled, such as by keeping in. a cool space, until it sets to a firm jelly. The latter is broken up, as by shreddingfor instance, and thoroughly washed to remove soluble salts. suchas potassium nitrate and any excess potassium halids. The wash "water is, of course, cool enough not to melt the pieces of The washed 6111111531011 is next remelted to 100 F. and 1050 parts of water soaked gelatin are thoroughly mixed into it, the temperature then being raised, say between 120 F. and 150 F, for instance, for a short time, say a few minutes. It is then cooled and set. It-is an example of the ammonia or alkaline type of develop ing-out emulsion.

Our sensitizing compounds and reducers may be incorporated together or sequentially in the emulsion or its ingredients at different stages of the above described process. They are most conveniently handled by dissolving them in a solvent which is inert with respect to the emulsion and simply acts as a vehicle to help in spreading the sensitizer and reducer throughout the emulsion.

The different gelatins sold for photographic emulsion-making may be used in the example given above, hard ones being very useful. The temperatures given are, of course, readjusted if the particular gelatin. employed has melting and setting points which deviate considerably from the usual ones, this adjustment being a matter of routine control.

Instead of employing gelatins which give emulsions of useful but lower sensitiveness even before the addition of our sensitizer and reducer, we may use practically inert gelatin. This may be prepared, for example, by treating active photographic gelatins with oxidizing agents. Dilute aqueous solutions of a peroxide, such as sodium peroxide (say from 5 to 10% by weight) may be intimately mixed into the gelatin and then washed when the oxidation has occurred. Such an inert gelatin, when mad-e into an emulsion by the above described process, produces little, if any, useful sensitiveness. But when our combination of a sensitizing compound and reducing compound is added, either to the emulsion, or to the gelatin before it is made into an. emulsion, highly sensitive developing-out emulsions are produced.

WVhen adding our combination of reducer and sensitizer they may be mixed with a little ethyl alcohol as a vehicle to enable their ready admixture with the other ingredients. One very useful way of employing our combination is to form a highly concentrated emulsion of silver halid in inert gelatin. IV hen the proper grain sizes and other char acteristics have been established, we may then stir into the emulsion gelatin containing our mixed sensitizing agents and reducing agents.

In the examples given above, the steps of treating with ammonia and warming of the emulsion may be, one or both, omitted. Our combination acts to increase the light-sensitiveness independent of such ripening steps. But we prefer to use them because the effect of either or both of them is to give a stronger initial sensitized condition which is multiplied or increased by using our sensitizing and reducing compounds. Moreover, it is desirable to have sufficient ammonia, or equivalent alkali present to form slightly alkaline emulsions.

In place of the colloids mentioned above, other colloids used in photographic emulsions may be employed. Moreover, the principle of the invention is applicable to silver chloride, as well as to silver bromide and silver iodide and to mixtures of any two or more of them.

IVhilethe theory of operation of our invention is not vital to the successful use of it' nevertheless, the following explanation of the action appears to be what takes place. First there is formed a. complex of silver halid and the sensitizer, such as a thiocarbamid. Next there is an interaction of silver halid and the sensitizer, such as thiocarbamid, to form small specks of silver sul fide in the silver halid grains. Of course, where selenium or tellurium sensitizing compounds are used, there are correspondingly form-ed specks of silver sellenide or telluride. Mixtures of these substances form corresponding mixed effects. These specks act as nuclei of silver deposition. These nuclei then become enlarged by the addition of metallic silver atoms from the reduction of silver halid by the small amount of cooperating reducer. This nucleating action prevents the slight fog which would be present if the reducer were used alone.

Having thus described our invention, what we olaim-- asonewi and. desire to secure by Letters Patent is:

1. A photographic emulsion comprising acolloid, particles of 'photographic silver salt suspendeditherein, and added sensitizing an d. reducing compounds uponwhich at least partof the light-sensitiveness of the emul'-- sion: depends, the sensitizing compound: contraining a divalent atom of the sulfur group directly joined-fby a double bond to a-single metalloid atom, to- Which at least another groupof atoms is attached.

2. A photographic developing-out gelatlIlO-SilVQP-htllltl emulsion of: the alkaline type-of relatively high light-sensitiveness, comprising aimixture of the constituents of a gelatino-si-lven halid emulsion of lower light-sensitiveness, and an added sensitizing compound andanadded reducing-compound, thedifference'between said: lower an (said high light-sensitiveness depending upon said last twonamed compounds.

A photographic emulsion comprising a colloid, particlesof photographic silver salt suspended therein and? coacting sensitizing and l reducing: substances upon which at least partof i the light-sensitiveness of the emulsion depends, the: amount of said coaoting substancesbeing less than the order of. 10 grains-per 130 pounds of emulsion andv in sufficient. to". cause. immediate fogging tendency.

4'. In theprocess'ofpreparing a developing-out colloid-sensitive-silver-salt emulsion, increasing. i the light-sensitiveness thereof by incorporating with the other constituents thereoti an independent sensitizing com.- pound: and: a coacting reducing compound.

5. Tnthc-proccss of; preparing a develop ing-out colloid silver-salt; emulsion of the a lkaline type of relatively high light-sensitiveness, comliiningz constituents of a colloidsensitive silver-salt: emulsion of lowerlightsensitivencss with. sufiicient enacting sensiitizing and reducing compounds toeflccthigli light sensitiveness, the sensitizing compound containing adivalent': atom of the" sulfur group directly joinedtbya double bond to a single inetalloid atom to whicl'r at least another group of 'atoms is attached.

6. Inthe process of preparinga developingfout gelatinmsilver-halid' emulsiom. in:

creasing the lightrsensitiveness thereof by.

thereof an independent sensitizing compound and a reducing compound, theamountiofsaid last two named. compounds being less than the order of 10 grains per. 130 pounds of emulsion and" being insufiicient. tocause immediate fogging tendency,

8. The process of preparing photographic gelatino'silver-halid emulsions, which com: prises substantially freeing. gelatinfromi-an-y sensitizing compounds originated therein, mixing a-se sitizingeompound anda reducing compound therein, and preparing a sensitive photographic emulsion from. said mixture. i

9. An intermediate for. use in making photographic emulsions. comprising an emulsion-forming colloid haying, incorpp= rated. therein an. independent sensitizing compound and coacting: reducing compound 10. The process of. making anintermediate for use in the. preparation of-photographie emulsions, which comprises incorporating. in anemulsion-forming. colloid an independent sensitizing compound. containing. a. divalent atom of the sulfur group. directly joined. by a double bond to a single metalloid atom to which at least another group: oi. atoms is attached, and alsoincorporating, thenein a reducing compound. 7

11. Theprocess of making an intermediate for use 'in the preparation of\ photog 'aphie gclatino-silver-halid emulsions,. which. com: prises substantially freeing gelatin. from sensitizing compounds and incorporating therein coacting sensitizing compounds and reducing compounds;

Signed at Rochester, day of June, 1925..

SAMUEL SHEPPARD. REUBEN 1i. PUNNEIT,

New York, this 11th 

